Bis-(3-triethoxysilylpropyl) tetrasulphane (TESPT) was employed for surface modification of iron sand for use in magnetorheological elastomers (MREs). The amount of TESPT was varied at five levels (2,4,6,8 and 10wt%) relative to iron sand content to assess the optimum amount of coupling agent for interfacial bonding and damping performance. Evidence that coupling had occurred between iron sand and TESPT was identified by Raman Spectroscopy and the grafting percentage was determined by thermogravimetric analysis. Subsequently, isotropic MREs containing unmodified and modified iron sand particles and natural rubber were prepared. Crosslink density assessment by swelling testing provided evidence that the tetrasulphane group of TESPT formed crosslinks with the rubber chains. The results exhibited the advantages of TESPT as a coupling agent between iron sand particles and rubber and also revealed that 6% TESPT content produced the highest crosslink density. The effects of the amount of TESPT on dynamic mechanical properties the morphological characteristics of the MREs were also investigated.

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The work presented here shows that the natural frequencies of constrained systems may be obtained from asymptotic models of corresponding systems where the constraints are replaced by artificial mass or moment of inertia of very large positive and negative values. This offers a convenient alternative to the current practice of using artificial elastic restraints of large stiffness, a concept introduced by Courant in 1943, to remove a limitation on the choice of admissible functions. Recent publications show that in order to control the error caused by approximating constraints with restraints of large stiffness, it is necessary to use both positive and negative stiffness values. However, the negative stiffness introduces instability near the lower modes of vibration and the magnitude of negative stiffness parameter used must be greater than the highest critical stiffness to ensure bounded results are obtained. The use of positive and negative artificial inertial parameters overcomes this problem as they do not introduce instability near the lower modes, allowing the natural frequencies of constrained systems to be delimited to any desired accuracy.

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